1. Field of the Invention
The present invention relates to an electric power steering apparatus that produces a steering assist force by an electric motor.
2. Description of Related Art
In a rack assist type electric power steering apparatus that provides a steering assist force through a rack shaft, the rotation of an output shaft in an electric motor is decelerated through a speed reduction mechanism composed of a pulley belt mechanism. The output rotation of the speed reduction mechanism is converted into the axial movement of a rack shaft through a ball screw mechanism, for example, surrounding the rack shaft (see Japanese Unexamined Patent Publication No. 62-4673 (1987), for example).
An advantage of this case is that a belt is interposed in a power transmission path between the electric motor and the rack shaft, so that shock loading and vibration from the rack shaft are not transmitted to the electric motor.
In order to reduce a torque transmission loss by the sliding of the belt, it is considered that toothed pulleys and a toothed belt are used for the pulley belt mechanism.
However, there is a case where vibration and noise are produced by the mesh of the teeth of the belt and the teeth of each of the pulleys at the time of steering, which are transmitted to a housing, and are propagated inside of a vehicle to be noise.